Phosphate ore flotation process



United States Patent Ofi ice 3,098,817 Patented July 23, 1963 Delaware No Drawing. Filed Oct. 28, 1960, Ser. No. 65,604 16 Claims. (Cl. 209-166) This invention relates to a phosphate ore flotation process wherein the primary objective of the process is to separate silica as completely as possible from the phosphate rock, while at the same time obtaining a high yield of the phosphate rock.

Most natural deposits of phosphate rock such as those found in Florida contain an objectionably high percentage of silica. Even very quite high grade phosphate ore may contain as much as silica by weight, and the more abundant ore deposits contain at least to 30% silica. Typical Florida ore (phosphate matrix) as mined will contain approximately one-third phosphate mineral, one-third silica or siliceous gangue, and one-third clay. In the processing of these ores, they are first subjected to washing and screening operations to remove the clay constituents as slime and to recover coarse, pebble concentrate. Deslimed undersize (essentially 'l4 mesh to +150 mesh) from the screening operations is then used as flotation feed. Because of the removal of clay, this material will contain an even higher percentage of silica than the matrix, and the silica content will therefore normally range from 40% to 65% Current practice for the treatment of washer plant undersize involves rough separation of the feed at about 35 mesh. The coarse fraction is conditioned with anionic collectors and treated on concentrating tables, spiral concentrators, or spray belts. The fine mineral fraction is subjected to the Crago or double-float process which utilizes two stages of froth flotation. In the first stage, a deslimed flotation feed of the raw rock is conditioned with caustic soda, fuel oil, and fatty acids, and the conditioned feed is subjected to froth flotation where a phosphate product is floated and the underflow (largely coarse sized silica) is discarded to waste. The product obtained from this flotation operation normally still contains so much silica that its phosphate grade (BPL) is too low to be of much practical value. Accordingly, this intermediate product is de-oiled by scrubbing with sulfuric acid followed by desliming. The de-oiled, de-slimed product is then subjected to a second stage of froth flotation in the presence of a strong cationic collecting agent, such as an amine, where the silica is floated and discarded to waste. The underflow of the second stage of flotation is the final phosphate product.

The foregoing process, while capable of producing a concentrate containing 6% or less of silica (insolubles) with a recovery of 78-85% of the phosphate values in the rock, nevertheless suffers from a number of inherent disadvantages from the standpoint of the complexity of the processing steps, number of processing units required, and the cost of the chemical reagents.

The desirability of providing a simplified and improved flotation process for separating phosphate rock from silica has been recognized for some time. One approach has been to attempt to find collectors for the phosphate rock or for the silica which are sufliciently selective to permit the desired concentration to be achieved in a single stage of flotation without sacrificing phosphate rock recovery or requiring an undue consumption of reagent. Since the silica is normally present in a substan tially higher percentage than the phosphate rock, it is difli cult to achieve a clean separation of the raw ore by an operation wherein the silica is floated. On the other hand, unless the coarse silica is first removed, it is equally difl'icult to achieve a satisfactory separation by floating the phosphate.

One of the principal objects of the present invention is to provide an improved flotation process for separating phosphate rock from contaminating silica. Another more specific object is to provide a process of the character described which is capable of achieving the desired degree of separation in a single flotation stage, as distinguished from the present double-float process. Further objects and advantages will be indicated and described in the following detailed specification.

This invention is based on the discovery that certain esters of ialphasulfo aliphatic acids are highly selective collectors for silica-containing phosphate ore flotation feeds. During the experimental work leading to the present invention, it was found that such collectors readily adapt themselves for a flotation process wherein the phosphate rock is floated while the undesired silica is depressed. It was further discovered that the selectivity of these collectors is so great that an acceptable phosphate rock concentrate can be prepared from the raw ore in a signle flotation stage. The fact that the esters of the alphasulfo aliphatic acids are effective for this purpose is particularly surprising in view of the fact that the corresponding alphauslfo aliphaticacids have little or no activity as collectors for phosphate rock.

Another discovery having particular utility for the beneficiation of phosphate ore containing silica and magnetic mineralization is the conjunct use of a synergetic combination of an ester of alphasulfostearic acid and a fatty acid as a collector to selectively float a phosphaterich concentrate containing minor amounts of magnetic minerals which are readily removed by subsequent treatment of the concentrate with conventional magnetic separators. The conjunct use of fatty acid or tall oil fatty acid with the collector of the invention has utility for the flotation treatment of Florida phosphate ore since it reduces the quantity required of the relatively more expensive ester.

In practicing the method of this invention, the silica containing phosphate ore is subjected to froth flotation in the presence of an ester of an alphasul-fo aliphatic acid. One preferred class of such esters is represented by the type formula:

In the above formula, R is an aliphatic group, such as an alkyl group, containing from 10 to 20 carbon atoms, and R is an aliphatic group, which preferably contains from 1 to 10 carbon atoms. For example, the aliphatic group may be an alkyl group, a hydroxyalkyl group, a sulfoalkyl group, etc.

Particularly good results have been obtained with esters of alph'asulfo stearic acid. For such an acid in the foregoing type formula R would contain 16 carbon atoms. Particularly outstanding result-s have been obtained with monoethylene glycol esters of this acid. One preferred subclass is the monoethylene glycol esters of alphasulfo stearic and palmitic acids where the R groups contain from 14 to 16 carbon atoms. Polyethylene glycol esters of alpha-sulfo fatty acids can also be used, but the longer chain length of the ester group has not been found to be of any particular advantage. Excessive size of the ester group may be a dis-advantage, and with respect to polyethylene glycol groups the molecular weight of the groups should not exceed about 500.

Among the specific esters of the alphasulfo aliphatic acids which are useful in practicing this invention are the following: the monoethylene glycol ester, the isopropyl ester, the Z-ethylhexanol ester, the sodium isethionate ester, and the polyethylene glycol esters referred to above. Such esters correspond with the foregoing type formula wherein R is primarily a hydrocarbon group, such as a saturated alkyl group, and it may include other functional groups, such as hydroxyl groups, ether groups, sulfo groups, etc.

This invention may be practiced in a manner analogous to the first flotation stage of the present double-float process. The crude phosphate ore will be prepared for flotation in the usual way, first being washed and sized, and then deslimed. The deslimed silica-containing phosphate ore flotation feed will then be subjected to froth flotation in the same kind of flotation equipment presently employed. Necessarily, the flotation feed will first be conditioned with the chemical agents, including a collector or collector combination of the type previously described, and also any auxiliary collectors or other chemical agents desired in the process.

It is useful to introduce sodium hydroxide or sodium carbonate as one of the conditioning reagents, and it has been found to be advantageous to employ a petroleum hydrocarbon fraction as an auxiliary collecting agent. For example, fuel oil or kerosene or both can be used. In general, the same hydrocarbon fractions useful in the first stage of the double-float process can be employed as auxiliary reagents in conjunction with the ester of the alphasulfo aliphatic acid. More specifically, one to three parts of a petroleum hydrocarbon fraction may he employed per part of ester.

As in the present process, the flotation is carried out in an aqueous medium. If desired, the pH of the flotation pulp may be adjusted by suitable acid or basic reagents, but this has not been found to be necessary. In fact, it is preferred to carry out flotation at a pH of approximately 7'-9 resulting from dilution of the conditioned pulp to flotation density. While more acid or basic pHs can be used, such pHs may have the disadvantage of either decreasing phosphate mineral recovery or producing undesirable froth characteristics.

The desired product or concentrate will be floated and removed in the froth or overflow, while the silica will be removed in the underflow or tailings. If desired, the concentrate can be passed to one or more additional cells as part of the same flotation stage without requiring the addition of further collector beyond the initial conditioning of the flotation feed. Kerosene or other petroleum fraction and/ or frothing agents may be introduced into the first or all of the cells, as indicated above, to modify frothing. The final product does not require any further concentration. It can simply be dewatered and stored 101 shipped as required.

By the procedure just described, a phosphate ore flotaas in the second stage of the present double-float process. For most commercial purposes, however, a product of satisfactory grade can be obtained by the single flotation stage procedure described in the foregoing specification wherein the primary collector is "an ester of an alphasul'fo aliphatic acid. This invention is further illustrated by the following examples.

EXAMPLE I In the practice of the invention, 500 grams (dry basis) of 35/ +150 mesh deslimed phosphate flotation feed containing silica or siliceous gangue is introduced into conventional laboratory conditioning equipment and the mineral pulp density is adjusted to -75 solids (by weight) by the addition of suflicient water. The following reagents are then added to the mineral pulp: (1) a primary anionic collector selected from the described class of esters of alphasulfo aliphatic acid or consisting of a combination of the preferred ester and a fatty acid or tall oil fatty acid at the rate of 0.50 lb. to 1.50 'lb. per ton of dry solids, (2) a petroleum hydrocarbon fraction such as kerosene or fuel oil at the rate of 1 to 3 parts per part of primary collector, and (3) NaOH or Na CO in stoichiometric excess with respect to collector to provide a conditioning pH of 8.0 to 9.5. The reagent-pulp mixture is then agitated in the conditioner for l to 2 minutes. While the chemical composition and surface condition of a phosphatic mineral and the intensity of the conditioning operation may permit primary collector attachment without added alkali, conditioning with NaOH and/or Na CO is generally preferred in practicing the invention.

The conditioned pulp is transferred to the cell of a conventional flotation machine and subjected to froth flotation for from 1 to 2 minutes. A phosphate-rich froth product (concentrate) is withdrawn from the cell, leaving a cell under-flow product or flotation tailings which is sufficiently low in phosphorus content to be discarded. The froth product may be returned to the cell and, with out the addition of collector reagent, cleaned one or more times by flotation to further reject gangue minerals, and thereby increase the phosphate content of the concentrate. Normally, tailings from the flotation cleaning operation(s). will contain sufficient phosphate to warrant their recirculation through the process stream (for the recovery of the contained phosphate values.

The above outlined procedure was employed in obtaining the data for all of the following examples.

EXAMPLE II A Florida phosphate ore containing 46.3% acid insoluble (silica) and 42.3% BPL was treated as outlined in Example I using a primary collector prepared by partial (83%) esteriflcation of alphasulfostearic acid with mogioethylene glycol. The flotation results are recorded in Ta le 1.

Table I Reagents, lbs/ton of feed Cleaner and rougher concentrates Test No. Percent acid insol. Percent BPL grade Percent BPL recovery Collector Fuel Oil Kerosene Cleaner Rougher Cleaner Rougher Cleaner Rougher tion feed containing in excess of 40% silica by weight can EXAMPLE III be processed to obtain a product containing not over 6% silica in combination with at least 85% of the phosphate of the flotation feed. For some purposes, it may be desired to reduce the silica content even further. Some further improvement can be obtained by subjecting the product to a cationic-type flotation wherein the silica is floated Table II below records the ifiotation results for the treatment of the same ore described in Example II. The collector comprises the same ester of alphasulfostearic acid described in Example II used in conjunction with Neo-Fat 42-12 (Armour), which contains approximately 45% oleic, 38% linoleic, 3% linolenic, and 14% rosin acids.

Table III below records the flotation results for the treatment of a low grade phosphatic beach sand, which illustrates the synergistic collector elfect obtained by the conjunct use of the ester described in Example 11 and Neo-Fat 94-04 (Armour), a red oil which contains approximately '83% oleic acid. The beach sand contained 1l1 3% BPL, 14-15% magnetic mineralization (mainly titaniferous magnetites, zircon, and r-utile), and a total acid insoluble content of about 80%. The concentrates produced were to be further upgraded by magnetic treatment for removal of magnetite, ilmenite, etc.

Table II Reagents, lbs./ton of feed Cleaner and rougher concentrates Test N0. Collector Percent acid insol. Percent BPL grade Percent BPL Fuel recovery E t N F Oil NaOH s er 42-12 Cleaner Rougher Cleaner Rougher Cleaner Rougher Table III Reagents, lbs./ton of feed Cleaner and rougher concentrates Test No. Collector Percent acid lnsol. Percent P20 grade Percent P105 recovery E t N F Fuel oil NazCOa Pine oil er 94-04 Cleaner Roughcr Cleaner Rougher Cleaner Rougher EXAMPLE IV and is selected from the class consisting of alkyl, hydroxy- The following data illustrates the improved flotation selectivity of the monoethylene glycol ester of alphasulfosteanic acid which is 67.9% esterified as compared to a crude tall oil containing 47.4% fatty acid and 45.7% rosin acids. The ore treated was a sample of Florida phosphate flotation feed which contained 52.45% acid insolubles and 38.33% BPL.

The alphasulfo fatty acids may be prepared as described in the copending application, Serial No. 840,541, filed September 17, 1959, now abandoned. In preparing the ester for use in the method of this invention, the usual esterification procedures are used. It is not necessary to obtain 100% esterification. Excellent results are obtained when the esterification appears to be between 60 and 90% complete, as measured by the water evolved during the esterification reaction and by titration.

While in the foregoing specification this invention has 'been described in relation to certain specific embodiments thereof and many details have been set forth for purpose of illustration, it will be apparent to those skilled in the art of froth flotation that the invention is capable of being adapted to additional embodiments and that many alkyl and sulfoalkyl groups, recovering the phosphate ore concentrate from the overflow, and removing the separated silica in the under-flow.

2. The process of claim 1 wherein R contains from 14 to 16 carbon atoms.

3. The process of claim 2 wherein said collector is a monoethylene glycol ester.

4. The process of claim 1 wherein said collector is an ester of alphasulfostearic acid.

5. The process of claim 1 wherein said collector is the monoethylene glycol ester of alphasulfostear-ic acid.

6. An ore flotation process, comprising subjecting a silica-containing phosphate ore to [froth flotation in the presence of a collector comprising a polyethylene glycol ester of an alphasulfo fatty acid wherein the fatty acid groups contain from 16 to 18 carbon atoms and wherein the polyethylene glycol group has a molecular weight of not over 500, recovering the phosphate ore concentrate from the overflow, and removing the separated silica in the underflow.

7. The process of claim 1 wherein the collector is the isopropyl ester of alphas-ulfostearic acid.

8. The process of claim 1 wherein the collector is the Z-ethylhexanol ester of alphasulfos-tear-ic acid.

9. The process of claim 1 wherein the collector is the sodium isethionate ester of alphasulfostear-ic acid.

10. The process of claim 1 wherein said collector is employed in conjunction with a petroleum hydrocarbon fraction.

11. The process of claim 1 wherein said collector is employed in conjunction with a free fatty acid.

12. The process of claim 1 wherein said collector is employed in conjunction with both a petroleum hydrocarbon fraction and a free fatty acid.

13. The process of claim 3 wherein said collector is employed in conjunction with both a petroleum hydrocarbon traction and a free fatty acid.

14. An ore flotation process, comprising subjecting a raw, deslimed, silica containing phosphate ore flotation feed to froth flotation in the presence of a collector selected from the group of esters of alphasulfo aliphatic acids represented by the type formula:

wherein R is an aliphatic group containing from 10 to 20 carbon atoms, and R contains from 1 to 10 carbon atoms and is selected from the class consisting of al-kyl, hydroxyalkyl and sulfoalkyl groups, said froth floation being carried out in an aqueous medium at a pH from about 6 to 8 and in the presence of at least one auxiliary collector selected from the group consisting of petroleum hydrocarbon fractions and long chain fatty acids, said flotation feed containing in excess of 40% silica by Weight, recovering the phosphate product fl'OIIl the overflow while removing the separated silica with the under-flow, thereby obtaining a phosphate product containing not over 6% silica in combination with at least 85% of the phosphate in said flotation feed.

15. The process of claim 14 'Wherein R contains from 14 to '16 carbon atoms and wherein said collector is a mono'ethylene glycol ester.

16. The process of claim 14 wherein said collector is the monoethylene glycol ester of alphasulifostearic acid.

References Cited in the file of this patent UNITED STATES PATENTS 2,185,541 Cohn Jan. 2, 1940 2,293,640 Crago Aug. '18, 1942 2,312,466 Erickson 'Mar. 3, 1943 2,433,258 Booth Dec. 23, 1947 2,806,044 Weil Sept. 10, 1957 2,927,691 Chapman Mar. 8, 1960 FOREIGN PATENTS 824,447 Great Britain Dec. 2, 1959 OTHER REFERENCES Journal of American Oil Chemists Society, volume 32, Number 6, June 1955, pages 370-372. 

1. 1N ORE FLOTATUON PROCESS, COMPRISING SUBJECTING A PHOSPHATE ORE CONTAINING SILICA TO FORTH FLOATION IN THE PRESENCE OF A COLLECTOR REPRESENTED BY THE TYPE FORMULA: 